Rotary snap action switching mechanism with locking means



Dec. 29, 1964 J. o. RoEsER 3,163,724

ROTARY SNAP ACTION SWITCHING MECHANISM WITH LOCKING MEANS Filed Aug'. l5, 1959 5 Sheets-Sheet 1 INVENT OR.

Dec. 29, 1964 J. o. Rol-:SER 3,163,724

ROTARY SNAP ACTION SWITCHING MECHANISM WITH LOCKING MEANS Filed Aug. 13, 1959 5 Sheetsfshee 2 ffy' 4 444, 4,3@ @11.

L\ mw 10E 4Z" 110g l i ki I INVENT OR.

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ROTARY SNAP ACTION SWITCHING MECHANISM WITH LOCKING MEANS Filed Aug. l5, i959 5 Sheets-Sheet 141 /7/ c 5 50@ 4. 30x J. @.j

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ll"In M M 645k HEL Dec. 29, 1964 J. o. RoEsER 3,163,724

ROTARY SNAP ACTION swITcHING MEcHANIsM WITH LOCKING MEANS Filed Aug. 13. 1959 5 Sheets-Sheet 4 @i147- .l o fe 4% 44 G u W 11W 66u lad ,IM A 'JM ii El f/-f INVENToR.

@f0- E'g 146 W/ Dec. 29, 1964 J. o. RoEsER 3,163,724

ROTARY sNAP ACTION SNITCHING MECHANISM WITH LOCKING MEANS f 16g 14m/54 Jaz/AA ,/AMNNN/ 544i g5( A H l @y United States Patent O 3,163,724 R'IARY SNAP ACTION SWI'ICIIING MEI-IANIFBM WI'IH LCKING MEANS .lohn 0. Reeser, Fark Ridge, Ill., assigner to Illinois 'fool Works, line., a corporation of Delaware Filed Aug. 13, 1959, Ser. No. 833,413 13; Claims. (Cl. 25Min-Iii) This invention is concerned with the art of electric switches, and more particularly with a detent locking mechanism and cooperating spring drive for insuring a snap movement from one position to another'.

It is well known that it is undesirable to have switches open and close their contacts slowly, as this causes arcing with resultant burning of the contacts and sometimes damage to related devices. Various types of snap switch mechanisms have been developed to insure rapid opening and closing of the switch contacts. This invention relates to a switch of the snap switch type, and more particularly to improved operating parts therefor.

It is an object of this invention to provide a superior snap switch mechanism.

It is another object of this invention to provide a snap switch mechanism which is compact and yet rugged.

A. further object of this invention is to provide a snap switch mechanism operable over a great number of switch positions.

It is a further object of this invention to provide a rotary snap switch mechanism.

A still further object of this invention is to provide a snap switch mechanism converting rotary motion to reciprocating motion for operating switches of the low travel or push button type.

Other and further objects and advantages of the present invention will be apparent from the following description when taken in connection with the accompanying drawings, wherein:

FIG. 1 is an elevational view of a preferred embodiment of the invention;

FIG. 2 is a cross sectional View thereof as taken substantially along the line 2 2 in FIG. 1;

FIG. 3 is a longitudinal sectional View on an enlarged scale through the operating mechanism, and corresponding to part of FIG. l;

FIG. 4 is a View similar to FIG. 3 showing the parts in a different position of operation;

FIG. 5 is a cross sectional View taken along the line S-S in FIG. :5;

6 is a cross sectional View along the line 6-6 in FIG. 3;

FIG. 7 is an exploded perspective View of the detent operating mechanism of the snap switch;

FIG. 8 isa fragmentary detail View showing the cam of the driver or driving plate;

FIG. 9 is a view similar to FIG. 5 showing a modification of the invention;

FIG. 10 is an exploded perspective view corresponding to FIG. 7 and showing the modification of FIG. 9;

FIG. ll is a plan view of the driver or driving plate of the modication;

FIG. 12 is a fragmentary longitudinal view through a modified form of the invention;

FIG. 13 lis a longitudinal sectional view through another modilication of the invention as taken substantially along the line 13-13 in FIG. 15;

FIG. 14 is a cross sectional view taken along the line 14-14 in FIG. 13;

FIG. 15 is a fragmentary cross sectional view taken substantially along the line 15-15 in FIG. 13;

FIG. 16 is a fragmentary longitudinal sectional view taken substantially along the line le-16 in FIG. 15.

ice

FIG. 17 is a front view of an encased modified switch unit;

FIG. 18 is a side view thereof;

FIG. 19 is a top view with the case or housing removed;

FIG. 2() is a vertical sectional view taken substantially along the line 2li- 2li in FIG. 19;

FIG. 21 is a vertical longitudinal sectional view along the line 21-21 in FIG. 17;

FIG. 22 is a vertical cross-sectional view along the line 22--22 in FIG. 21;

FIG. 23 is a vertical cross-sectional View along the line 23-23 in FIG. 20;

FIG. 24 is a vertical cross sectional View looking toward the front of the switch unit substantially along the line 24x-2d in FIG. 21;

FIG. 25 is an exploded horizontal sectional view along the line 25-25 in FIG. 24;

FIG. 26 is a perspective view of the locking element of FIGS. 19-25; and

FIG. 27 is an axial sectional view of the gear-locking member taken along the line 2.7-27 in FIG. 25.

Referring now in greater particularity to the drawings, and lirst to FIGS. 1 8, there will be seen a rotary snap switch identiiied generally by the numeral 26. The switch comprises a front or detent plate 22, and intermediate plate or bulkhead 24, and a back plate 26. The detent plate 22 is spaced forwardly oi the bulkhead 24 by four relatively short spacers 2S, and the hack plate 25 is spaced a greater distance behind the bulkhead by four relatively long spacers Sii aligned with the spacers 2S. Through bolts 12- extend through the detent plate, the spacers 2li, the bulkhead 2d, the spacers 30, and the 'back plate 26, the heads of the bolts being recessed or countersunk in the detent plate Nuts 3d are threaded on the ends of the bolts.

rIhe detent plate 22 is provided with a threaded bushing 36 which may he secured in place by conventional means such as hrazing, or expanding or peening in position. The detent plate further is provided with a plurality of small holes 38 spaced along an arc concentric with the bushing 36. In the illustrative embodiment now under consideration, there are four such holes spaced at twenty degrees apart. The holes 33 comprise locking holes, as will be brought out hereinafter.

A driving shaft itl extends rotatably through the hushing 36 and to the rear of the detent plate 22. The driving shaft 4) may be rotated by any suitable or desirable means, including the usual manually engageable knob (not shown). The driving shaft is provided at its end with a reduced diameter tip d2. A driving plate or driver 44 is iixed adjacent the end of the driving shaft on a section 45 of intermediate diameter, and preferably is held in place by brazing at 48.

The driver 44, as may be seen in FIGS. 5, 7 and 8, cornprises a segment of a circular plate somewhat greater than a semicircle. The segment is cut oil or deiined by a terminating chord 45, and a driver linger or lug 4S extends rearwardly from the center of this edge in an axial direction. Diametrically opposite to the nger 48 the driving plate or driver 44 is provided with a cam slot 59. This slot tapers from a maximum` width radially of the driver at the center of the slot, as at 52, to a minimum dimension at the opposite ends thereof. The ends are formed as circular arcs. The slot extends twenty degrees in either direction from the center thereof, in accordance with the twenty degrees spacing of the locking holes 38. f v

The switch further includes a driven shaft Se journaled in the bulkhead 2d and haci; plate coaxial with the driving shaft 4d. The forward end `oi the driven shaft 54 is slightly enlarged at S6 and is provided with a coun- 3 shaft 54h. The switch operators or levers g2b are in this instance driven by cams Slob. A. knob 1l@ is iixed on the extending end of the shaft 4Gb.

A bushing i12 is rotatable on the shaft, being positioned by a washer M4 against a shoulder H6 of the shaft. The driven or latch plate llb is secured to the bushing, as by brazing. The driving or driver plate llll-b is fixed on the shaft 4612 adjacent a shoulder' llS thereon, and against the back ot the iront wall 22h.

In operation, the knob llt? is turned to turn the shaft Mtb, S-tb, whereby the cams 961) operate the levers @2b to vary the condition of actuation of the various switches (not shown). Since the driven or latch plate tit'lb is at first secured against movement by the tip 3211 of the plunger 75l; iitting in one of the series of holes 38h, the spring @6b tends resiliently to hold the driver plate l/lb, and hence the shaft dnb, 54]) in its initial position. rlhus, the shaft is turned against a spring force until it has turned far enough tor the cam slot 5Fl-b to retract the plunger lob against its internal spring Sab. The spring retarding force thus is removed, and the shaft moves to the next switch position, the tip S2!) subsequently snapping into the next successive hole .'ib. As will be apparent, the fact that the shatt is initially turned against a spring resistance tends to preclude accidental turning of the shaft, as by physical shocks, or inadvertent manual engagement of the knob. Furthermore, the shaft cannot come to rest in an intermediate position, or any other position oif of a proper switch position, since the driven or latch plates will stop in position only at one of the holes 3811, and the shaft will be automatically aligned with the driven plate by virtue of the spring dnb acting between the driver plate and the driven plate dnb.

A further embodiment of the invention is shown in FlGS. 13-16. This embodiment is substantially the same as that shown in FlG. l2, but is used alternatively thereto in accordance with different requirements, such as space requirements for the switch unit. Again, similar numerals are utilized to identify similar parts, the sul'rx c being applied in this instance.

One essential distinguishing feature of this embodiment relative to the embodiment or FlG. l2, is that the driving and latching mechanisms are not mounted on the shalt. Instead, a gear l2@ (NGS. 13 and l5) is xed on the shaft forwardly of an intermediate supporting wall or web 2de. The driving and latching mechanisms are radially oilset therefrom, being mounted on a shalt M2 (FEGS. l5 and 16). The driver is provided over a portion of its periphery with gear teeth lid meshing with the teeth of the gear 12d. Accordingly, the driver 44e is turned exactly in accordance with turning of the shalt f-tlc, 55de, but without being mounted on this shaft. Operation of the switch 7de of FlGS. 13-15 is similar to that of the embodiment of HG. l2, except for the offsetting of the driving and latching mechanisms, as previously noted.

There is a further variation in connection with the last embodiment of the invention, as shown in FlG. 16. Thus, there is a solenoid SL25 having a winding 128 on a coil form 130. The front portion of the coil form projects through the web 24C as at 32.. The solenoid lZi further has a fixed core portion i134, by means of which it is mounted on the back wall 2de. The solenoid also vhas a movable core portion or armature or slug i3d re -ently urged away from the iixed core portion by a spring 13S mounted in a recess in the front part of the iixed core portion i3d. The armature or slug i3d carries a pin ldd which projects into a recess on the back side of the driver plate 44C. ln accordance with one practical embodiment of the invention, there is only one such recess M2. Hence, the pin Mt) of the solenoid T12-5 tends to hold the switch in one particular predetermined position. The solenoid may be energized from some external source (not shown) whereby to unlock the switch from the predetermined position. Once the switch has been so unlocked, it may be moved from one to another of several positions of switch actuation, and will be locked by the solenoid pin only when returned to the aforesaid predetermined position. rl`he extent of rotation of shaft lille is limited by a disc 39 (FIG. 13) fixed on the shaft and having a relieved section cooperable with a stop pin 141 fixed on the front wall 22e.

Reference now should be had to FlGS. 17-27 in connection with an improved form of the invention. The invention in this series of drawings includes a case or housing 1.44 having a molded-on bottom 146 of plastic material or the like. This material underlies a floor 148 in the casing which supports the individual switches tied. Lead wires lSll from the individual switches project through the floor M8 and through the molded bottom As will be understood, the molded bottom herrnetically seals the case.

The embodiment of FIGS. l7-Z7 is in many respects quite similar to that in FlGS. tl-16, and also partakes of features of the previous embodiments oi the invention. Thus, in order to avoid proli .ty of description, similar numerals have been utilized with the addition of the suttix d. The driving shaft tld and driven shaft 54a' again are integral, and a knob lltd of more or less teardrcp shape is shown on the end of the driving shaft for turning the same. The driven shaft 54d again is provided wih cams 96d for operating the pivoted levers 92d for converting the rotary motion of the shaft 5dr] to reciprocating or oscillating motion for operating the push-button type switches Stia'. Rotation of the driving shaft lo' again is limited by means of a dise 13%! (see particularly FiG. 24) having a cut out section therein receivinf7 a xed stop pin lf2-icl mounted in the front wall 22d. A driving gear lllld is lixed on the driven shaft Sdn', as in the last previous embodiment of the invention.

ln the present instance, he driverdlld is provided with teeth tiled entirely around its periphery. The driver again is provided in its rear face with a recess 142e! receiving a pin lfilld, extending from the slug or reciprocated member luft of a solenoid Med mounted on the intermediate wall 24d and on an intermediate wall or web 125 spaced rearwardly thereof.

The solenoid lied serves to latch the driver 44d at a predetermined rest or zero position. Hence, the switch unit cannot be switched or moved from this position until atter the solenoid lloc has been energized. As will be apparent, a series of apertures ltd could be provided, whereby the solenoid would latch the driver in any predetermined position.

The present form of the invention is distinguished from the prior embodiment in the form of the latch mechanism. More particularly, the driver 44d is provided on its face with radially disposed, arcuately spaced teeth E52 (see particularly FGS. 23, 25 and 27). The teeth are arranged to present alternate crests 154 and valleys or oots 156. The teeth are higher at their radially outer ends as indicated at lSS in FlG. 27, and tapered to a minimum height at their radially inner ends as indicated at The shape and size of the teeth are such as to result in tivo diametrically opposite plateaus lidi. rEhe presence of these plateaus does not interfere with the movement of the driver member since the degree of rotation thereof is limited by the disc llild and pin Mie' which limit the rotation ot the shaft Mld, 54d.

Confronting the teeth ld?. is a locking detent lod. he detent los comprises a rectangular bloei; (see particularly FIG. 26) disposed diametrically of the driver 44d. The detent li is provided on the front tace ol the block lo@ with a wedge shaped tooth loll running trom end to end thereof. The tooth is congured to tit between adjacent teeth l5?. on the lace of the driver member 44d.

The detent ldd is mounted in a slide block ltl (see particularly FIG. 25) held on the baci: side of the face 22d by means such as screws t7?, extending through the tace and threaded into the slide block. The slide block is provided with a channel lfs receiving the base or block arcanes 166 of the detent ldd, and is further recessed at 176 and 17S for receiving the driver member 44d and the face teeth lSZ thereon. The stub shaft Mld receiving the driver ddd extends through the slide block litl, and through a central aperture l@ in the detent.

The detent 164 is provided on the back face thereof with a pair of recesses i822 spaced on opposite sides of the shaft opening lili?. These recesses receive the front ends of a pair of helical springs ld, the rear ends of Which are seated in complementary recesses 186 in the A detent block l'itl.

The cooperation of the detent slide box, the detent plunger, the face teeth on the driver, and the locking pin for the driver is shown in somewhat exploded nature in FIG. 25. Normally, the parts are related as shown in FIGS. 19 and 20, and the various switches der! are held in predetermined conditions of open or closed. When the solenoid 12de' is energized to retract the pin todo', the parts are capable of being moved. Turning of the knob llltld tends to rotate the driving shaft dhd and the integral driven shaft 54d. This tends to cause the gear tif/:tid to rotate the gear toothed driver 44d. Y However, such rotation is resisted by the spring pressure of the tooth of the detent plunger. However, sufficient pressure on the knob lltld will cam the tooth 168 out of the valley between adjacent teeth, and over the intervening crest. soon as the detent or detent plunger has passed such eres (it will be understood that it simultaneously passes a pair of crests on diametrically opposite sides of the driver) the springs force the detent tooth into the next succeeding valley, whereby to snap the driver from one rotational position to the next, the driven shaft 54d simultaneously being snapped to the next succeeding position through the gear teeth 12M and the gear 12M. The cams 96d and levers 92d thus change the conditions of the individual switches in accordance with the shape of the cam, some of the switches being changed, and others remaining as before. ln any event, the action is a snap action, which is highly desirable from a standpoint of switch contact life, and from a point of precisely controlling the operation of the devices which may be connected to the individual switches 86d.

The particular detent mechanism just described has the virtue of impossibility of dead centering. Thus, the driver cannot dead center relative to the detent plunger, and hence the driving and driven shafts cannot be left in such position that the switches are anything but fully opened or fully closed. Accordingly, incorrect combinations of circuits cannot be made. The detent mechanism just described has the further desirable characteristics of being able to develop rather heavy torque through the cam action of the detent tooth, as forced by the springs ld. This allows the switch unit to operate satisfactorily even though rather substantial friction might be developed in the moving parts, as through corrosion or extreme ternperature or pressure variations.

Additionally, the switch unit has rather high inherent frictional resistance to movement. The various lever arms have a certain amount of friction about their mounting shaft, the bearings of the driving and driven shaft present a certain amount of friction, the cams and follower levers present friction (as well as the force necessary to close the switches Sed), and a certain amount of friction is introduced by the detent mechanism itself. All of this friction and resistance to rotation readily is overcome by a substantial margin through the use of the detent mechanism of FlGS. 17-27. Even if the operator were deliberately to try to place the operating knob in a middle position, the detent mechanism would positively shift the driven shaft in one way or the other to a definite switch position. Furthermore, as will be obvious, there is no chance for one switch position to be skipped inadvertently, since the detent mechanism tends to lock rather positively in any given position.

Aa mm im amm-.ent the crests of the face teeth on the driver, and also sharp. As a result, full torque is upon passing of a dead center position of the detent tooth v and the driver' face teeth.

Various changes in structure will no doubt occur to those skilled in the art, and will be understood as forming a part of this invention insofar as they fall within the spirit and scope of the appended claims.

The invention is claimed as follows:

l. A snap action device comprising a driving shaft, a driven shaft coaxial with said driving shaft and extending axially rearwardly therefrom, fixed base means rotatably mounting said driving and driven shafts, a driver fixed on said driving shaft, a driven member on said driven shaft to the rear of said driver, torsion spring means acting between said driver and said driven member and resiliently tending to bring said driver and said driven member into predetermined rotational alignment, said fixed base means having fixed locking formations thereon axially forwardly of said driven member, locking means on said driven member extending forwardly therefrom in the direction of said driver and selectively engageable with said locking formations to lock said driven member and said driven shaft in fixed position, rotation of said driving shaft and said driver applying tension on said spring means, and said driver having means thereon effective after predetermined rotation of said driver operatively to engage and to shift said locking means axially of said shafts and thereby to release said locking means from one of said locking formations whereby said spring means rotates said driven member and said driven shaft with a snap action to bring said driven member back intosaid predetermined rotational alignment with said driver.

2. A snap action device as set forth in claim l wherein the driver and the driven means comprise a pair of plates spaced apart axially of the shaft, the fixed locking formations on said base means being on the opposite side of said driver from said driven member, the locking means on said driven member extending axially past said driver for engagement with said locking formations, said driver having cam means thereon engageable with said locking means upon rotation of said driver to shift said locking means axially of said shafts and thereby to release said locking means from one of said locking formations.

3. A snap action device as set forth in claim 2 wherein the cam means comprises a slot in said driver, said slot having a relatively large radial dimension `at the center thereof, and a lesser radial dimension at either end, said locking means projecting through said slot and having cooperating cam means thereon.

4. A snap action mechanism comprising a driving shaft,

a driven shaft coaxial with said driving shaft and extending axially therefrom, fixed base means rotatably mounting said fixed driving and driven shafts, a driver fixed on said driving shaft, a driven member on said driven shaft, torsion spring means acting between said driver and said driven member and tending resiliently to maintain said driver and said driven member in predetermined rotational alignment, said xed base means having xed locking formations thereon, locking means on said driven member shiftable axially of said shafts and selectively engageable with said locking formations to lock said driven member and said driven shaft in fixed position, rotation of said driving shaft and said driver applying tension on said spring means, said driver having means thereon effective after predetermined rotation of said driver to shift said locking means axially of said shafts and thereby t0 release said locking means from one of said locking formations whereby said spring means rotates said dn'ven member and said driven shaft with a snap action to snap said driven member into said predetermined rotational alignment with said driver, a plurality of xed switch means respectively spaced along said driven shaft from said driving shaft in parallel with one another, and movable means moving with said driven shaft and cooperable ensayos il with said fixed switch means to operate said plurality of switch means.

5. A snap action mechanism as set forth in claim 4 wherein the xed switch means comprises a plurality of switches spaced along the driven shaft, and wherein the movable means cooperable therewith comprises an equal plurality of projections on said driven shaft, said projections being successively rotationally displaced.

6. A snap action mechanism as set forth in claim 5 wherein the movable means further includes a plurality of pivotally mounted levers respectively engaged by said projections and urged against said switches.

7. A snap action mechanism as set forth in claim 4 wherein the fixed switch means comprises a plurality of arcuately spaced fixed switch contacts, `and wherein the movable means cooperable therewith comprises a switch arm fixed on said driven shaft.

8. A snap action device comprising a base, a driver rotatably supported from said base, a driven member rotatably supported from said base coaxial with said driver and axially spaced therefrom, means for rotating said driver, torsion spring means acting between said driver and said driven member and resiliently tending to maintain said driver and said driven member in a predetermined position of rotational alignment, said base means having locking means thereon spaced on the opposite side of said driver from said driven member, locking means on said driven member projecting axially past said driver and engageable with the locking means on said base to loclt said driven member in iixed position relative to said base, rotation of said driver applying tension to said spring means, and means on said driver operable on the locking means on said driven member after predetermined rotation of said driver relative to said driven member to operatively release the leciti-ng means on the driven member from the locking means on the base, whereby said spring means rotates said driven member into said preetermined position of rotational alignment with said driver, said driven member locking means comprising means on the driven member providing a seat opening axially of the driven member and radially displaced from the center of rotation thereof, and a spring loaded plunger mounted in said seat.

9. A snap action device as set forth in claim 8 wherein the driver and the driven member `comprise a pair of plates, and wherein the means on the driver for releasing the locking means on the driven member from the locking means on the base comprises a cam slot through which the locking means on the driven member projects.

l0. A snap action device as set forth in claim 8 wherein the driver and the driven member comprise a pair of axially spaced parallel plates, wherein the plunger is provided with a tapered section, and wherein the releasing means on the driver comprises a cam slot through which said plunger projects, the tapered section of the plunger engaging the driver in the vicinity of the cam slot for camming said slot.

11. A snap action device as set forth in claim 10 wherein the locking means on the base comprises a series of rcuately spaced apertures, and wherein the plunger is rovided with a tip extending beyond the tapered section and seiectively received in said apertures.

12. A snap action device comprising rotatable shaft sans, base means rotatably mounting said shaft means, a driver rotatably carried from said base means and rotatable wih said shaft means, a driven member coaxial with said driver and extending rearwardiy therefrom, torsion spring means acting between said driver and said driven member and resiliently tending to maintain said driver and said driven member in predetermined rotational alignment, said base means having locking formations thereon forwardly of said driven member, locking means on sai driven member extending forwardly therefrom in the direction of said driver selectively engageable with said loclr'ng formations to lock said driven member in fixed position, rotation of said shaft means and of said driver applying tension on said spring means, and said driver having means thereon effective after predetermined rotation of said driver operatively to release said locking means from one of said locking formations whereby said spring means rotates said driven member with a snap action to bring said driven member back into predetermined rotational alignment with said driver, the shaft means comprising a singie shaft, and the driver, the driven member, the torsion spring, and the locking means serving as a latching device for the shaft.

13. A snap action device as set forth in ciaim l2 wherein the driver and the driven member are radially offset from sai-d shaft means, and further including gear means connecting said shaft means to said driver.

bio;

References Cited by the Examiner UNETED STATES PATENTS 770,166 9/04- Cox 20G-70 771,98? 10/04 MacKintosh 20D-166 1,038,567 9/12 Greengard 200-166 1,702,287 2/29 Williams 20G-70 X 2,023,2l9 12/35 Beamer 200--65 2,023,235 12/35 Le Count 74-112 X 2,460,000 1/49 Flanagan 74-112 X 2,789,167 4/57 Erbstosser 200-18 2,804,526 8/57 Ganbatz 200--153 2,828,372 3/58 Bulgin 200-17 2,906,832 9/59 Foster et al. 20018 2,908,777 10/59 Brown 200-65 X 2,908,790 10/59 Pigone 200--153 FOREIGN PATENTS 310,343 12/55 Switzerland. 807,300 1/59 Great Britain,

BERJ'VARD A. GlLHl-EANY, Primary Examiner. MAX L. LEVY, Examiner. 

1. A SNAP ACTION DEVICE COMPRISING A DRIVING SHAFT, A DRIVEN SHAFT COAXIAL WITH SAID DRIVING SHAFT AND EXTENDING AXIALLY REARWARDLY THEREFROM, FIXED BASE MEANS ROTATABLY MOUNTING SAID DRIVING AND DRIVEN SHAFTS, A DRIVER FIXED ON SAID DRIVING SHAFT, A DRIVEN MEMBER ON SAID DRIVEN SHAFT TO THE REAR OF SAID DRIVER, TORSION SPRING MEANS ACTING BETWEEN SAID DRIVER AND SAID DRIVEN MEMBER AND RESILIENTLY TENDING TO BRING SAID DRIVER AND SAID DRIVEN MEMBER INTO PREDETERMINED ROTATIONAL ALIGNMENT, SAID FIXED BASE MEANS HAVING FIXED LOCKING FORMATIONS THEREON AXIALLY FORWARDLY OF SAID DRIVEN MEMBER, LOCKING MEANS ON SAID DRIVEN MEMBER EXTENDING FORWARDLY THEREFROM IN THE DIRECTION OF SAID DRIVER AND SELECTIVELY ENGAGEABLE WITH SAID LOCKING FORMATIONS TO LOCK SAID DRIVEN MEMBER AND SAID DRIVEN SHAFT IN FIXED POSITION, ROTATION OF SAID DRIVING SHAFT AND SAID DRIVER APPLYING TENSION ON SAID SPRING MEANS, AND SAID DRIVER HAVING MEANS THEREON EFFECTIVE AFTER PREDETERMINED ROTATION OF SAID DRIVER OPERATIVELY TO ENGAGE AND TO SHIFT SAID LOCKING MEANS AXIALLY OF SAID SHAFTS AND THEREBY TO RELEASE SAID LOCKING MEANS FROM ONE OF SAID LOCKING FORMATIONS WHEREBY SAID SPRING MEANS ROTATES SAID DRIVEN MEMBER AND SAID DRIVEN SHAFT WITH A SNAP ACTION TO BRING SAID DRIVEN MEMBER BACK INTO SAID PREDETERMINED ROTATIONAL ALIGNMENT WITH SAID DRIVER. 